Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.69   13.852%   $63.4042   $63.40   $63.40   $63.40  
  Purchase #2 $62.61   11.270%   $69.6661   $69.67   $69.65   $69.70  
  Purchase #3 $30.64   5.711%   $32.3899   $32.39   $32.40   $32.40  
  Purchase #4 $249.53   8.863%   $271.6458   $271.65   $271.65   $271.60  
  Purchase #5 $101.29   6.505%   $107.8789   $107.88   $107.90   $107.90  
  Purchase #6 $208.39   5.245%   $219.3201   $219.32   $219.30   $219.30  
  Purchase #7 $127.82   5.562%   $134.9293   $134.93   $134.95   $134.90  
  7 purchase totals = $835.97       $899.2343   $899.24   $899.25   $899.20